With the increasing demand of various communication services, wireless customer premise equipments (CPEs) are necessary in the heterogeneous environment of Long Term Evolution (LTE) networks. The LTE CPEs are used for broadband data access and data service conversion between Wi-Fi, wired LANs and LTE [1]. The data are transmitted through CPEs to the LTE networks. To provide high-speed data transmission and better coverage, multiple-input multiple-output (MIMO) antennas are usually adopted in wireless CPEs. Also, the technique of carrier aggregation (CA) is employed in LTE-Advanced to aggregate fragmented spectrum from different bands into a larger spectrum resource for further enhancing the data transmission capacity. As a result, multiple sets of antennas and bandpass filters operating at various frequencies are involved in the RF front-ends of CPEs. On the other hand, the CPEs are often required to be low profile and as compact as possible for easy installation. Therefore, it is of great interest to integrate the antenna and bandpass filter to increase the integration level of RF front-ends.
In recent years, some integrated designs of filters and antennas were proposed. A typical method to design filtering antennas is to replace the last stage of filter network with an antenna radiator, which results in high integration. However, in some designs, extra filtering circuits are inserted to the antenna feeding networks, causing extra insertion loss and degrading antenna gains. To solve this problem, filtering antennas without extra filtering circuits are proposed in [14]-[15] and the in-band gains are not affected. However, the reported filtering antennas above are restricted to single-band operation, and they are difficult to fulfill the required dual-band specifications of CA.
Recently, some dual-band filtering antennas were reported. In some technical solutions, a dual-band antenna and filter are designed separately and then cascaded together to form a dual-band antenna-filter module. For example, two dual-band planar filtering antennas were proposed. The rectangular patch generates two orthogonal polarizations at the two bands in one example. And the TM10 and TM30 modes of the patch were employed to enable dual-band operation in another example. However, the operating frequencies of these two antennas cannot be controlled individually. Besides, the peek gains of them within the two bands are only −1.8/−4.0 dBi and 1.1/3.8 dBi due to the extra insertion loss caused by the feeding network. In a further example, a U-slot patch antenna is integrated with a dual-mode stub-loaded resonator through electromagnetic coupling. Good performance including harmonic suppression is obtained. However, it employs a 2-layer PCB structure and cannot meet the low-profile requirement. Furthermore, there are no specific out-of-band radiation nulls to improve skirt selectivity.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.